The authors describe a four-channel-audio and two-channel-video signal transmission system that constitutes an optical wavelength division multiplexed light-emitting diode (LED) 850/1300-nm network for use in home video, television, or any other video distribution system. Since the pulse frequency modulation scheme was used to modulate the LED, excellent linearity was achieved compared with direct intensity modulation of the light source. The SNR was also improved by increasing the modulation index, although the CNR was decreased by the transmission loss of the optical fiber and the insertion loss of the optical multiplexer. >

New Optical Audio And Video Signal Transmission System For Home Appliances

This paper describes a new type of factory communication system using optical fibers. This new type of optical fiber SSB data communication system consists of a pair of optical transmitters, each transmitter constructed using an edge-emitting LED (ELED), a pair of optical receivers and a pair of single-mode-optical fibers, each having a length of 12 km. A pair of 12 channels are assigned to SSB data with frequencies of 12 kHz through 60 kHz in the lower frequency band on the up-going link, and of 72 kHz through 120 kHz in the higher frequency band on the down-going link, respectively. The transmitter and receiver are housed in a transmitter-receiver unit. When the transmission was experimentally carried out, the spurious noise was below -50 dB on each channel, and SNR was more than 60 dB. This system can be used to send status and voice data for the electrical and mechanical machines in place of power line communications.

New type of optical fiber SSB analog data communication system using edge-emitting LEDs coupled to single mode optical fibers

This paper describes a single-mode(SM) optical fibre SSB data communication system for use in place of power-line data transmission. In the optical transmitter, SSB data is fed through the squarewave frequency (SWFM) modulator to the edge-emitting LED (ELED) module. The light beam of the ELED module is fed to the SM optical fibre having a length of 12km. In the optical receiver, the light beam received through the SM optical fibre is detected by the PIN photodiode module, and fed to the SWFM detector to obtain the double-pulse frequency modulation (DPFM) signal voltage. The DPFM signal voltage at the output of the SWFM detector is fed to the low-pass filter (LPF) to obtain analogue SSB data. When the transmission was experimentally carried out, the spurious component was as low as −50–−70 dB and the SNR of SSB data as high as more than 65–70 dB. The optical transmitter and receiver were attached to the conventional analogue SSB data communication system to constitute a new optical fibre analogue SSB data communication system. During the field test utilizing the new system, the crosstalk and SNR were 60–70 dB and 60–70 dB on each channel, respectively. Copyright © 1999 John Wiley & Sons, Ltd.

New type of optical fibre analogue SSB data communication system using edge-emitting LED coupled to single-mode optical fibre

従来,制 御信 号 や デー タ の伝 送 システ ムには平衡 ケー ブ ルや同軸 ケー ブル な どが使 用 されて き た。 これ らの 既存 シ ステムで1~2kmPl上 の距 離 に制御 信 号を 伝送す る場合, 伝送品質,伝 送 容量 な どに 問題 があ り,特 に劣悪 な使 用環 境では電磁 誘導 な どの 影響 によ り伝送 品質 の劣 化,伝 送 シ ステム設計 の複 雑化 な どが 問題 とな る(1)。 一方 ,光 フ ァイバ は電気 雑 音 か らの干 渉 を受 け難 い特長 があり,超 高周 波帯 での広 帯 域性 及 び伝送 につ いての 高容 量性に特長 があ る。 これ らの特 長 を活 か して,長 距離,高 速度,大 容量 等 の通 信 に は レーザ ダ イオ ー ドとシ ングル モ ード光 フ ァイバ の組 み 合わ せ が広 く使 用 され てい る(2)。 しか し,産 業 用情 報 の 伝送 で は,工 場 内或 いは機器 間 で制 輝信号 やデ ータ を伝 送 す るな ど,2km以 下 の近距 離 に制 御信号 やデー タ を伝 送 す る場合 が多 く,発 光 ダイオ ー ドと 多モー ド光 フ ァイバ,或 い は,発 光 ダ イオ ー ドとプ ラスチ ック光 フ ァイバ の 組 み 合わ せ によ り構 成 され た伝送 システ ムに も,十 分 な技 術 的,経 済 的価値 があ る と認 め られ る(3) {4) 。 従来 の 同軸 ケ ー ブル で1~10MHzの 帯 域 を有 す る映像 信号 を伝送 す る場 合,特 性 補償 用 中継 増幅器 を 挿入 せず に伝 送 で き るケー ブル 長 は せ いぜ い200mで あ る。 一 方 ,光 フ ァイ バ では100MHz以 上の帯 域 を有 す る多 重 映像 信号 を,中 継 増 幅器 な しに2kmの 距離 へ容 易 に伝 送 で きる(5)。 更 に,同 軸ケ ーブ ル に比較 して,光 フ ァイ バ は比帯 域 が極 め て広 く,筆 者 らの実 測 によ れば,2km の 伝送 で も1~100MHzの 周 波数 範囲 でFM画 像 信 号 を多重 伝送 した場 合,伝 送 特 性 は ほぼ 均一 で あ る。 ま た, 短 距離 の光 フ ァイバ 伝送 方式 で は,電 磁波 を使 って空 間 伝 送 す る場合 の よ うな混信 や法 制上 の帯 域 制限 が全 く存 在 し ない特 徴 があ る。

Parallel Transmission of Square-Wave FM Multifrequency Control Signal Using Optical Fiber

Described is part of the encoding and decoding circuits for use in the narrow-angle PSK system. Data of the normal QPSK system is in the sender fed to a divide-by-four frequency counter to make the shift angle narrow. Narrow-angle PSK data is in the receiver fed to a pair of frequency doubler to make the shift angle wide so that normal QPSK data can be obtained. Narrow-angle PSK data is transmitted from the sender to the receiver through the optical fiber. Data was at 1.432 MHz during the transmission on the optical fiber and the maximum phase angle was 90 degrees. By the use of the frequency counter and doublers, the synchronizing in the receiver was drastically improved and stabilized. >

Encoding and decoding circuits for narrow band PSK data transmission via optical fiber

In the square-wave PFM system for transmission of TV programmes through optical fibres, square-wave PFM pulses are generated at the transmitter with a relatively low centre frequency, whereas double-frequency equal-width narrow pulses are produced in the receiver before the demodulating low-pass filter, at both the rising and falling edges of the transmitted pulses. The use of the frequency-doubling technique in such a system results in narrow transmission bandwidth and high receiver sensitivity, thus prolonging the transmission distance significantly as compared with ordinary PFM. In the experiment, the system is operated at 1.3 μm with multimode fibre having bandwidth 700 MHz km, a laser diode as optical source and a PIN/FET as detector. It can effectively transmit the high-quality broadcast TV programme with accompanying sound channel to a distance of 50.7 km. Experimental results are: receiver sensitivity −40 dB m, weighted SNR for video 59.3 dB, differential gain and differential phase less than 1% and 1°, respectively.

Kan Jia-Xi

Papers

Frequency-doubling PFM system to prolong the distance of optical fibre TV programme transmission